Explain rapid closure of a Venus flytrap
Trace stimulation of trigger hairs to rapid movement of the modified leaf lobes.
Section 15.2 · Control and coordination in plants
A Level; Cambridge International Biology 9700, 2028–2030. Written answers are self-checked; this is not practical-skills certification.
Before you begin
- A control pathway links a stimulus, receptor, coordination system and response.
Work on paper. Try each question before revealing help, and explain why your method works.
Quick readiness check
What is stimulated to initiate the rapid response?
What you will learn
- Describe stimulation of hairs on the lobes of a Venus flytrap
- Explain how a rapid signal changes lobe curvature to close the trap
Venus flytrap response
| Feature | Meaning |
|---|---|
| Stimulus | Hairs on the trap lobes are stimulated |
| Signal | Electrical changes spread across the modified leaf |
| Movement | Lobe curvature changes and the trap snaps shut |
| Context | Rapid leaf movement is not a muscle contraction |
Build the mechanism
A Venus flytrap has modified leaf lobes bearing trigger hairs. Stimulation of these hairs generates electrical changes that spread through the trap. The lobes are mechanically pre-stressed; changes in cell and tissue forces alter their curvature and produce a rapid snap closure. This is a fast movement of a plant organ, not muscle contraction or growth by cell division.
Keep the sequence precise
Distinguish the stimulus, electrical signal and mechanical movement. The trap closing is not proof that a plant has nerves or muscles; its cells coordinate the response through plant electrical and mechanical properties.
Pause and explain
A student concludes that a Venus flytrap has muscles because it closes rapidly. Correct the inference.
Worked example
A touch to a trigger hair is followed quickly by the lobes snapping shut. Identify stimulus, signal and response.
Show the worked solution
- The hair stimulation is the stimulus.
- Electrical changes spread and the lobes change curvature.
Answer Stimulus: trigger hair is touched. Signal: electrical changes spread through the leaf. Response: the mechanically primed lobes snap shut.
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Write your answer and reasoning first. Use a hint only if you are stuck. The model solution is for self-checking; your written work is not automatically marked.
Explain how stimulation of a trigger hair can lead to trap closure.
Give me a hint
Name the first event, then follow each link in order.
Compare my reasoning
- Hair stimulation initiates electrical changes.
- The signal changes lobe mechanics and curvature.
Stimulation of a trigger hair initiates electrical changes that spread through the modified leaf. These changes alter lobe curvature, and the pre-stressed lobes snap shut.
Look for these in your work
- Mechanism stated
- Steps linked in order
A plant trap closes slowly over several days as it grows towards a support. Is this the rapid Venus flytrap response? Explain.
Give me a hint
Use the terms in the question and state what changes.
Compare my reasoning
- Compare the time scale and mechanism.
- The syllabus example is rapid movement after hair stimulation.
No. Slow growth towards a support is a growth response. The Venus flytrap example is rapid closure following stimulation of hairs on its lobes.
Look for these in your work
- Evidence interpreted
- Biological direction explained
A student concludes that a Venus flytrap has muscles because it closes rapidly. Correct the inference.
Give me a hint
Apply the mechanism to the new context without adding unsupported claims.
Compare my reasoning
- Movement alone does not prove muscle tissue.
- Plant leaf mechanics generate the response.
Rapid movement does not show that the plant has muscle. Electrical and mechanical changes in the modified leaf alter lobe curvature and produce closure.
Look for these in your work
- Mechanism applied
- Limits preserved
Common mistakes
- Calling the trigger hair a nerve
- Describing closure as slow directional growth
What can you explain now?
What is stimulated to initiate the rapid response?
Compare with the explanation
Trigger hairs on the trap lobes
Their stimulation initiates electrical and mechanical events leading to closure.
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Make it stick
How do trigger-hair stimulation and leaf mechanics combine to close the trap?
If you needed the solution, close it and solve the problem again from a blank page. A correct answer is stronger when you can explain the reason for each step.